Developer for electrophotography



Aug. 4, 19 4 E. K. KAPRELIAN DEVELOPER FOR ELECTROPHOTOGRAPHY 2 Sheets-Sheet 1 Original Filed July 3, 1957 E/G 4 F/G 5 VOLTAGE SOURCE 1m LED 5 EMMA ADNE RED BLUE GREEN \WH/TE fmyb wew g- 1954 E. K. KAPRELIAN DEVELOPER FOR ELECTROPHOTOGRAPHY Original Filed July 3, 1957 2 Sheets-Sheet 2 United States Patent 3,143,508 DEVELOPER FGR ELECTRGPHOTOGRAPHY Edward K. Kaprelian, 29 Riveredge Road, Red Bank, NJ.

Original application July 3, 1957, Ser. No. 669,866, now Patent No. 2,940,847, dated June 14, 1960. Divided and this application Mar. 14, 1960, Ser. No. 14,777

6 (Ilaims. (Cl. 252-621) This application is a division of my copending application, Serial No. 669,866, filed July 3, 1957, entitled Electrophotography, now Patent 2,940,847.

This invention relates to improved methods and means for electrostatic color photography or color printing and is specifically directed to the developers employed in the production of color electrophotographs.

In ordinary electrostatic photography or printing there is formed on an insulating surface an intermediate electrostatic image, corresponding in potentials to the light values of the original object, and this electrostatic image is rendered visible by dusting with a suitable powder which adheres selectively to the surface in a pattern corresponding to the electrostatic image. A description of this process may be found in US. Patent 2,297,691, issued Oct. 6, 1942, to C. F. Carlson.

It is also possible to practice electrostatic photography by illuminating a layer of normally insulating photoconductive powder which is located in an electrical field. In this case powder lying in an illuminated area becomes charged and is attracted away to a region of opposite polarity. A description of this process may be found in US. Patent 2,758,939, issued Aug. 14, 1956, to M. L. Sugarman.

In the electrophotographic processes of these and other patents of the prior art the action is essentially that of an ordinary monochromatic or black-and-white system. The basic image is one rendered in monochrome, and it is possible, by utilizing color separation techniques, to produce color prints or photographs by superimposing in proper registry separation images employing properly chosen dyes or pigments.

In contrast with previously known systems the present invention produces the color image directly in a single step without the use of separation images. In the practice of this invention the color image is produced by the selective migration of charged color toner particles in an electrical field according to the color or wavelength of the light.

One of the objects of this invention is to employ the principles of electrostatic electrophotography in the production of color prints.

Another object is to provide a relatively simple, direct and low cost arrangement for the production of color photographs, prints, posters and signs.

Still another object is the provision of a method and means for the continuous production of color prints.

Still another object is to provide color developer particles for producing color electrophotographs.

These and other objects will become apparent from the specifications and drawings in which FIG. 1 shows in cross section one form of photoconductive color particle.

FIG. 2 shows in cross section another form or" photoconductive color particle.

FIG. 3 shows in cross section still another form of photoconductive color particle.

FIG. 4 shows in cross section still another form of photoconductive color particle.

FIG. 5 shows in cross section one form of a nonphotoconductive color particle.

FIG. 6 shows in cross section another form of nonphotoconductive particle.

FIG. 7 shows diagrammatically the arrangement of photoconductive color particles prior to exposure in one method of the invention.

FIG. 8 shows diagrammatically the arrangement of the color particles of FIG. 7 after exposure.

FIG. 9 shows diagrammatically the arrangement of photoconductive color particles prior to exposure in another method of the invention.

FIG. 10 shows diagrammatically the arrangement of the color particles of FIG. 9 after exposure.

FIG. 11 shows diagrammatcally the arrangement of non-photoconductive color particles prior to exposure in still another method of the invention.

FIG. 12 shows diagrammatically the arrangement of the color particles of FIG. 11 after exposure.

FIG. 13 shows diagrammatically the relationship of elements for printing from the color image resulting in FIG. 12.

FIG. 14 shows diagrammatically the final arrangement of the color particles in FIG. 13 after exposure.

The color toner particles shown in FIGS. 1 to 6 are typical of the image forming elements which can be utilized with the method of photography described herein. In the use of any of these particles the essential action is that in a layer of mixed color particles, those particles of a given color will migrate or, if desirable, react oppositely by remaining unmoved when subjected to light of the given color.

The color toner particle 10 of FIGS. 1 and 2 comprises one or more bits 12 of a suitable photoconductor surrounded by a layer or coating 14 of dyed gelatin or similar material. Typical photoconductive materials include selenium, zinc oxide, cadmium sulfide, cadmium telluride, anthracene, and sulfur. Actually any photoconductive powder may be used, and it is preferred that the particle sizes fall in the range of 2 to 30 microns. The dyed layer may consist of any suitable dye in gelatin, wax, vinyl or silicone resin, cellulose ester or similar material in a thickness of from 4 to 25 microns. The powdered photoconductor may be mixed with the dyed layer ma terial together with a solvent and then dried while being agitated, as by a warm air blast. Spraying of the photoconductor-solvent-dye layer mixture into a heated chamber will also yield suitable particles. In order to increase the photographic speed of these particles it may be necessary to add to the dye layer a small amount of a suitable salt to reduce the electrical resistance of the layer and thereby permit more rapid charging of the particle.

FIG. 3 shows a toner particle 16 comprising a central core 18 which may consist of a clear, transparent glass or plastic bead carrying a transparent photoconductive layer 20 and an outer, dyed, transparent layer or coating 22. The multiple layers may be formed in the manner described in connection with particle 10, or the photo conductor layer may be evaporated onto the glass head. A head diameter of 3 to 30 microns, a photoconductive layer of 5 to 60 microns thickness and a dyed layer of 4 to 25 microns thickness will yield satisfactory particles in the 21 to 250 micron diameter range.

FIG. 4 shows a toner particle 24 comprising an inner capsule 26 containing a liquid dye 28, a photoconductor layer 20 and a dye layer 22. The dye filled capsule 26 preferably in the diameter range of 3 to 20 microns, may be produced in the manner described in the US. Patents 2,730,456, 2,730,457, and 2,714,074, issued to B. Green. The photoconductor layer may be added by evaporation and the dye layer applied as described in connection with FIGS. 1 and 2.

FIG. 5 shows a toner particle 30 comprising a colored glass or plastic head 32 covered with a thin layer 34 of a conducting material. In the case of glass heads a layer of fused transparent tin oxide is suitable. In the case of layer.

plastic beads a thin transparent layer of evaporated metal is preferred, although treatment with so called anti-static solutions is also suitable. As shown in FIG. 6, it is also possible to produce beads 36 which comprise a solid, substantially spherical body 38 of tin oxide or other transparent electrically conducting materials which are suitably colored in the mass. As in the case of other particles a diameter of between 3 and 40 microns'is preferred for particles of this class, although for some applications larger particles are suitable.

In the practice of color electrophotography as set forth in the present invention the following series of steps or their equivalent must be performed in the. approximate order shown:

(1) Establishment of an electrostatic field.

(2) Production of a light image.

(3:) Charging or discharging of colored particles, which are in the electrostatic field and on which the light image 1s received, in accordance with the color and pattern of the image.

(4) Migration of either the charged or the discharged particles of step 3, corresponding to the image, to a new surface or a new location.

(5) Fixing or receiving onto a final support surface migrated or non-migrated particles, or both, to form a final fixed color image.

It will be noted that with some arrangements to be described certain steps, particularly those enumerated (1) and (2) above, can be reversed in order.

FIGS. 7 and 8 show one arrangement whereby additive color unages can be produced by the used of colored photo-conductive toner particles. A glass or similar transparent plate 40 carries a transparent electrically conductmg layer 42 of NESA glass or thin evaporated metal. An upper electrode plate 44 spaced from plate 40 by any suitable distance from 1 or 2 millimeters to several centlmeters, carries at its lower surface a particle receiving layer 46 to be described below. A suitable source 48 of DC. voltage, connected to layer 42 and electrode 44 is provided with suitable switching means 50. A negative potential of from 300 volts to 5000 volts is applied to electrode 44 depending upon its spacing from plate 40 and the characteristics of the particles employed. In this arrangement particles 10 and 16 of the type shown in FIGS. 1, 2 and 3, colored red, green and blue, are employed. A substantially uniform layer of these primary colored particles is placed on conducting glass 42.

'For purposes of illustration a single layer is shown in FIG. 7; the layer may be 3 or more particles deep and can be applied by simply cascading onto surface 42, or by spraying, or by applying with a roller.

After exposure to light of various colors the toner.par-

ticles migrate to the position shown in FIG. 8. Where additive type, which for proper viewing as a print must be transferred to a black base, for example a sheet of black surfaced paper or plastic material. The image may be transferred to such a base by the usual electrostatic means or through action of 'a suitable adhesive supported on a suitable base sheet in which case it be-' comes the image support. The image which remains on surface 42 is a negative image, also of the addi- .tive type and may be also transferred to a black base.

This may be the desired image if color quirement of the process.

As shown, in the arrangement of FIGS. 9 and 10 this reversal is a re- Fixing of the image may be accomplished by method can also be adapted to subtractive color photography. Here the arrangement of electrodes is similar to that of FIGS. 7 and 8 and the parts have been numbered correspondingly. In this modification, transparent colored particles 52 of the type shown in FIG. 4 are employed, containing cyan. magenta and yellow dye, the primary subtractive colors, at centers 28 and colored red, green and blue, the primary additive colors, respectively at layers 32. Initially particles 52 are randomly distributed on surface 42 in a layer 3 to 4 particles deep, although in FIG. 9 they are shown in a single layer with regular distribution for the purpose of explanation. When subjected to a light image some of the particles will be moved upwardly depending upon the color of light. Where red strikes a red jacketed particle 24 containing cyan dye resting on surface 42 the resistance of the photoconductive layer is reduced, the particle becomes charged and migrates to surface 46. The photoconductive layer of a blue jacketed yellow containing particle struck by red light will remain unchanged in electrical resistance and will not acquire a charge from surface 42 and will not migrate. Neither will a green jacketed magenta containing particle migrate when struck by red light. Blue light will cause blue jacketed yellow containing particles to migrate while leaving the red and green jacketed particles unmoved, and green light will cause green jacketed magenta containing particles to migrate while leaving the cyan and yellow jacketed particles unmoved. Exposure to white light causes particles of all three jacketv colors to migrate to surface 46. Following exposure the red jacketed cyan containing particles, blue jacketed yellow containing particles and green jacketed magenta contain ing particles will delineate on surface 46 red, blue and green areas of the original subject. These particles are transferred, preferably by electrostatic means, to a transparent base or to a white reflective base coated with a suitable transparent absorbent layer, such as gelatin. A similar sheet is laid over the particles, and the resulting sandwich subjected to pressure as, for example, by passing between a pair of rollers. The pressure causes the particls to burst, and the dye previously contained within them is absorbed by the absorbent surface of the base material. The two base layers are stripped apart and the particles of debris removed by means of brushing or washing. The resulting image will be a color reversal of the original.

If the transfer is made from surface 42 after exposure the resulting color image will be a positive color photograph.

FIGS. 11 to 14 illustrate still another Way in which the invention may be employed to produce subtractive color images. Here the particles 34 are non photoconductive and possess the characteristics described in connection with FIGS. 5 and 6. A layer of particles 34, 3 or 4 deep, is deposited on a photo-conductive layer 60 of selenium or other suitable material supported on an electrically conducting base 62 of brass, aluminum or the like which is connected to one terminal of a voltage source such as described in connection with FIG. 7. Spaced from and parallel to the surface 60 is a sheet of glass 64 carrying at its under side a layer 66 of transparentelectrically conducting material which is connected to the second terminal of the high voltage source. The layer of particles is exposed by light passing downwardly through sheet 64 and conductive layer 66 onto particles 34.. For a given color or spectral band of exposing light one or more of bead colors, which are cyan, magenta or yellow, will .transmit the light to the selenium layer below. The selenium layer thereupon becomes conducting, the transmit- 'ting bead becomes charged and migrates upwardly to layer 66.

As shown in FIG. 12, red, green and blue light exposure results in migration of magenta and yellow, cyan and yellow, and cyan and magenta particles, respectively,

to form subtractive color layers. In order to assure that the particles apply themselves in substantially layer form it is preferred that the sizes and conductivities oi the particles be controlled. By making the cyan particles somewhat smaller and utilizing a relatively lower conductivity surface 38 over the core, these particles will migrate first to form a cyan layer. By increasing the size of the magenta particles and increasing the electrical resistivity of their surface the magenta particles will migrate next to form the second layer. Preferably the yellow particles are the largest and possess the highest resistivity, thereby being deposited last. While the diagrammatic representation in the drawing has been that of a single layer for the sake of simplicity, it should be borne in mind that multiple layers of the type described represent the actual structure. Where white light reaches the particle layer all particles migrate to surface 66. Where no light strikes the particle layer no particles migrate.

The intermediate image appearing on surface 66 is next used for printing as shown in FIGS. 13 and 14. The image on surface 66 is projected onto a selenium plate 70-72, similar to the plate 60-62, through a transparent conducting plate 74-76 similar to plate 6466 onto color particles 34. During exposure these particles migrate to surface 76 to form a subtractive color image corresponding to the original subject of FIG. 11.

In some modifications of the method with which the color developer of the invention may be employed, as described in Patent 2,940,847, the toner particles are suspended in a liquid dielectric such as light mineral oil or carbon tetrachloride.

It is apparent that the color particles shown and described could be varied With regard to construction and choice of materials by those skilled in the art.

I claim:

1. A toner particle for developing electrophotographic images consisting of an inner portion of a liquid dye material, an encapsulating layer of a transparent solid surrounding the liquid core, a second layer of a transparent photoconductor and a substantially continuous outer layer of light filter material capable of transmitting a restricted portion of the spectrum.

2. A toner particle as claimed in claim 1, said restricted portion of the spectrum corresponding substantially to that of a primary color.

3. A toner particle as claimed in claim 1, said restricted portion of the spectrum corresponding substantially to that of two primary colors.

4. A toner particle as claimed in claim 1, the diameter of the encapsulating layer being between 3 and 20 microns.

5. A toner particle as claimed in claim 1, the color of the liquid dye corresponding to that portion of the spectrum transmitted by the outer layer.

6. A toner particle as claimed in claim 2, the color of the liquid dye corresponding to that portion of the spectrum absorbed by the outer layer.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,691 Carlson Oct. 6, 1942 2,618,551 Walkup Nov. 18, 1952 2,714,074 Green July 26, 1955 2,730,456 Green Jan. 10, 1956 2,730,457 Green Jan. 10, 1956 2,758,939 Sugarman Aug. 14, 1956 2,899,335 Straughan Aug. 11, 1959 2,939,804 Schossberger et a1 June 7, 1960 2,962,375 Schafiert Nov. 29, 1960 FOREIGN PATENTS 557,577 Canada May 20, 1958 564,712 Canada Oct. 14, 1958 

1. A TONER PARTICLE FOR DEVELOPING ELECTROPHOTOGRAPHIC IMAGES CONSISTING OF AN INNER PORTION OF A LIQUID DYE MATERIAL, AN ENCAPSULATING LAYER OF A TRANSPARENT SOLID SURROUNDING THE LIQUID CORE, A SECOND LAYER OF A TRANSPARENT PHOTOCONDUCTOR AND A SUBSTANTIALLY CONTINUOUS OUTER LAYER OF LIGHT FILTER MATERIAL CAPABLE OF TRANSMITTING A RESTRICTED PORTION OF THE SPECTRUM. 